1. Field of the Invention
The present invention concerns a gear train of an automatic five-speed transmission for a vehicle and more particularly a gear train for obtaining five steps of forward moving speed and one step of backward moving speed according to driving conditions.
2. Description of Related Art
Conventionally, an automatic transmission for a vehicle includes a planetary gear unit connected between a torque converter and a driven shaft, which planetary gear unit comprises sun gears, a plurality of planetary gears, a planetary carrier for carrying the planetary gears, and a ring gear.
A plurality of clutches and friction elements are controlled to selectively grip the gears of the planetary gear unit so as to obtain a target speed. As is well known, such a conventional automatic transmission has an insufficient fuel consumption ratio or power or driving performance particularly in a high speed engine. Hence, there has been proposed a multistage control of speed in order to maximize the performance of a high speed engine.
Meanwhile, the multi-stage speed control of a transmission is preferably required using a minimum number of friction elements to facilitate the speed control. In addition, it is preferable to minimize the number of the friction elements in order to reduce volume and weight. In this respect, U. S. Pat. No. 5,112,285 discloses a multi-stage speed control of a transmission, wherein a speed change may be obtained by shifting the frictional grip from one element to another. This patent requires a large number of friction elements thereby increasing the volume and weight of the vehicle.